Chilling



CHILLING Filed April 26, 1930 INVENTOR W W W tb vywu W ATTORNEY jg FeedPatented Apr. 7, 1936 UNITED STATES PATENT OFFICE 6 Claims.

This invention relates to the chilling of fluids and in particular tothe reduction of temperature of oil for the purpose of precipitatingtherefrom substances, such as wax, that may be precipitated by reductionof temperature.

It is an object of this invention to provide a method and processcapable of effecting intense cooling by means which are definitelycontrollable to afford uniform continuous reduction of temperature andwhich are nevertheless simple, economical and of high efiicien'cy.

While this invention is applicable to the chilling of fluids generally,it will be described by way of illustration in connection with' thereduction of temperature of oils in connection with the dewaxingthereof. In so far as this invention is applied to the dewaxing' ofoils, it is immaterial from what source the oil is derived, inasmuch asthe oil may be crude petroleum oil, or a fraction, such as a distillateor residue thereof, or vegetable oil, or animal oil, or oil produced inthe destructive distillation of carbonaceous material or shale. The formof apparatus and method herein set forth are particularly adapted to thede- Waxing of fractions of parafiinor mixed base crude oils at lowtemperatures for the production of low cold test lubricating oil.

In reducing the temperature of the oil to precipitate wax therefrom,sudden cooling or shock chilling is disadvantageous. The oil should becooled gradually in order to have the'wax precipitate out in thephysical form best suited to the'removal thereof from the oil and toproduce an oil of superior cold test. Where oil is cooled by coming incontact with a chilled surface, the chilled surface with which thewarmoil comes in contact should not be more than approximately F. colderthan the oil in order to avoid shock chilling and to preventaccumulation of wax on the chilled surface.

According to the method and apparatus of this invention, the dewaxing ofoils may be accomplished in a continuous and relatively rapid manner,and at uniform rate of cooling without shock chilling. The waxprecipitated from the oil is thrown down in a form well suited forremoval as by centrifugal force, and an increased yield of dewaxed oilis produced which is of improved cold test.

It has been found that the separation of wax from oil can be promoted bymixing therewith a substance which is a solvent for" both the oil andwax while the mixture is warm, but is a solvent for the oil only whenthe mixture is chilled. Thus, in the practice of this invention, it isdesirable to mix a certain amount of solvent with the oil prior tochilling. For example, a solvent such as naphtha may be mixed with oiland a solution formed by bringing the mixture to- 100 F., and uponreducing the temperature to 40 F. wax will be precipitated from thesolution. The naphtha can be recovered by distillation after separationof the wax from the solution. While it may be desirable to mix a certain.amount of solvent such as naphtha with oil in dewaxing oil according tothis invention, it is to be understood that the word oil as used both inthe specification and claims is regarded as covering oils either mixedor unmixed with a solvent.

Heretofore, it has been proposed to chill oil prior to treatment thereoffor the removal of wax therefrom, by bringing the warm wax-containingoil into heat exchange relation with cold oil flowing from thattreatment and thereby partly cool ing the wax-containing oil, and thenbringing the partly cooled oil in an intermediate step and a separatefinal step into heat exchange relation with liquid volatile refrigerantto further cool the oil. It has also been proposed to cool the warm oilby heat exchange with cold dewaxed oil mixed with warm dewaxed oil, andthen by heat exchange with cooling medium cooled by liquid volatilerefrigerant, and then finally to bring the wax-containing oil so partlycooled into direct heat exchange relation with liquid volatilerefrigerant. These methods involve loss of cooling effect of the dewaxedoil because, in order to secure a steady supply of cold dewaxed oil thatis not subject to fluctuations which would cause shock chilling, no morecold oil flowing from the wax separation step can be safely used thanthat which occurs at the minimum rate of production, thus wasting abouttwenty per cent. of the cooling effect of the cold dewaxed oil. Moreoverthe wax bearing oil which has been cooled by cold dewaxed oil is notsufficiently cooled according to the above processes so that theintensely cold dewaxed oil can be brought directly from the waxseparation step into heat exchange with the wax bearing oil withoutshock chilling, but must have its intense cold tempered either bywarming it or by mixing warm dewaxed oil therewith, with resultant lossof efficiency. These methods also require an intermediate cooling stepbetween the step in which dewaxed oil is used and the step in whichliquid volatile refrigerant is brought into heat exchange relation withthe wax-containing oil at the minimum pressure used.

It is a feature of this invention that the warm wax-containing oil iscooled, by being brought into heat exchange relation with cold dewaxedoil, to a temperature (e. g., 25 F.) which is within a few degrees ofthe lowest temperature (e. g., 40 F.) desired for the precipitation ofwax, and which is sufiiciently low for the production of oil ofcommercially acceptable cold test, and which is so low that cooling tolower temperatures when oil of especially low cold test is desired, maybe effected by direct heat exchange with liquid volatile refrigerant ina single step, all of the cooling being effected without shock chilling.

Important features of this invention are that the dewaxed oil used as acooling medium in the cooling of wax-containing oil, is further cooled,prior to use as a cooling medium, and then it is used to reduce thetemperature of the wax-containing oil to a low temperature as abovestated, and that all of the cold dewaxed oil coming from the dewaxingoperation may be employed in heat exchange relation with the warmwax-containing oil, and that the temperature of the cold dewaxed oilcoming from the dewaxing operation need not be raised prior to such usethereof, either by mixture with warm oil or otherwise. A further featureof this invention is that the dewaxed oil used as a cooling medium mayconsist of oil coming directly from the dewaxing operation and furthercooled, or of oil that has been passed in heat exchange relation withwarm oil and so warmed and then re-cooled; or of a mixture of suchfurther-cooled oil and such re-cooled oil.

Advantageously, in the practice of this invention, all of the dewaxedoil flowing from the wax separating operation is passed to a coolingoperation preparatory to passing it in counterflow in heat-exchangerelation with wax-containing oil to be chilled, and a regulated quantityof warm dewaxed oil that has passed in heatexchange relation withwax-containing oil is added to the cold dewaxed oil flowing from theseparating operation to the cooling operation; and the resulting mixtureof dewaxed oil is cooled to a temperature which is preferably below thetemperature of the dewaxed oil flowing from the dewaxing operation. Thevolume of warm oil so added is so regulated as to compensate for thereduction in volume caused by the removal of the wax from the oil in thewax separating operation and for heat given off in the solidifying ofthe wax during cooling of the wax-containing oil. This is importantbecause if the heat absorbed from the warm wax bearing oil not only inlow ering its temperature but also in withdrawing the latent heatincident to precipitate the wax is greater than the capacity to absorbheat of the cold dewaxed oil flowing countercurrent and in heat exchangetherewith, the cold dewaxed oil will be warmed more rapidly than thewarm wax bearing oil is cooled, thus producing such lack of uniformityof rate of cooling and temperature gradient that shock chilling andinefficiency will result. The volume of cold dewaxed oil used as acooling medium is thus regulated in relation to the volume ofwax-bearing oil being chilled therewith, so that there will not only besuflicient volume of cold oil to lower the temperature of the waxbearing oil at approximately the same rate as cold dewaxed oil is warmedbut also suflicient additional volume temperature gradient that therewill be no shock chilling and maximum efiiciency will be obtained.

Important features and advantages of this invention are that the coolingof wax-containing oil by the use of dewaxed oil as a cooling medium, asabove described, is capable of effective regulation whereby shockchilling is avoided, and the wax-containing oil may thereby be broughtto a temperature at which it may be at once dewaxed to produce valuableoil or it may be at once, without intermediate cooling and withoutshock-chilling, further cooled by being brought into heat exchangerelation with liquid volatile refrigerant to a temperature so low thatseparation of wax will produce oil of very low cold test.

The steps comprising this invention may be employed separately and whenso employed constitute separate parts of this invention. They may alsobe employed conjointly and when so employed cooperate with one anotherto produce special advantages resulting from their cooperative relation.

Other and further objects, features and advantages of this inventionwill be apparent in consideration of the accompanying drawing which is adiagrammatic view of apparatus embodying this invention and whereby thisinvention may be practiced.

Warm wax bearing oil may be stored in tank it prior to chilling. Wherethe oil is mixed with a solvent such as naphtha prior to chilling, thesolution may be blended in tank I0. Preferably, this solution is made ata temperature of approximately 100 F. in order to effect substantiallycomplete solution. The warm wax bearing oil or solution, which latterwill also be referred to as oil, may then be pumped by pump II from tankIi] by lines l2 and I3 so as to enter a series of heat exchangers l4,l5, l6, l1, I8, [9, 20, and 2| wherein the oil is progressively chilledby heat exchange with cold dewaxed oil. The heat exchange is indirect,that is, without resultant mixing of warm wax-bearing oil with the colddewaxed oil. The wax bearing oil flows between said heat exchangers bylines 22. From the last heat exchanger 2| in this step of the chillingprocess, the partially chilled wax bearing oil may pass by line 23 toheat exchanger 24 where it is subjected to a second and last step ofchilling by direct heat exchange with an intense refrigerant such asammonia vapor. Thus, for example, warm wax bearing oil may be graduallychilled to about -25 F. during the first step by heat exchanged withcold dewaxed oil and then cooled to about 40 F. by direct heat exchangewith compressed ammonia released at a pressure of six pounds per squareinch absolute during the second step.

The chilled wax bearing oil passes from heat exchanger 24 by line 25through control valve 26 and supply line 21 to a wax separating device28 which is here shown diagrammatically as a centrifuge. While the useof a centrifuge is preferable according to this invention, any other waxseparating device may, of course, be used. Connected with supply line 21is a standpipe 29 and tank 30 in which there is a float 3| forregulating the control valve 26, thus efiecting automatic control of theflow of chilled wax bearing oil into wax separator 28. Wax separatedfrom the oil by the wax separator 28 may be discharged from separator 28through line 32 to tank 33 Where it may be accumulated and stored.Dewaxed oil discharged from the wax separator 26 may be conducted byline34 to tank 35.

The cold dewaxed oil in tank 35 is chilled and used as a refrigerant forthe Warm wax hearing oil according to this invention as follows: Colddewaxed oil in tank 35 passes by line 36 to pump 31 from which it isdischarged through line 33 into cooler 39. In addition to cooler 39 asecond cooler 4| is shown having a lower temperature than cooler 39 asit is preferable to chill the dewaxed oil in two steps. The dewaxed oilpasses from cooler 39 to cooler 4| by line 49. In cooler 39 chilling maybe accomplished by 2.1- lowing ammonia vapor, for example, to vaporizetherein at a pressure of 15 lbs. per square inch absolute. In cooler 4|chilling may be accomplished by allowing ammonia to vaporize therein ata pressure of only 6 lbs. per square inch absolute. From cooler 4| thechilled dewaxed oil is conducted by line 42 to heat exchanger 2| andflows through the coils thereof in heat exchange relation with the waxbearing oil. From heat exchanger 2| the oil passes successively throughheat exchangers 29, |9, |8, l7, |6, I5 and I4, being conducted betweensaid exchangers by lines 43.

The dewaxed oil which has been warmed by virtue of having passed throughthe above mentioned heat exchangers in the counterflow with the warm waxbearing oil is discharged from heat exchanger |4 through line 44 to thetank 45. A part of this warm dewaxed oil can be rechilled according tothis invention for further use as a refrigerant by pumping it by pump 48back to the tank 35 through lines 46 and 41. The rate of return flow ofthis warm dewaxed oil to tank 35 may be regulated by a valve 49 which iscontrolled by a float 59 in tank 35. The rate of flow of chilled dewaxedoil through heat e'xchangers |4 to 2| and withdrawn from tank 35 by line36 is greater than the flow of cold dewaxed oil from the wax separatorinto the tank 35 by line 34. It is thus apparent that all of the coldWax free oil from wax separator 28 is used to chill the incoming waxbearing oil. The level of the oil in tank 35 automatically controls byfloat 5|] and valve 49, the amount of warm dewaxed oil that must beadded to the cold dewaxed oil flowing into the tank 35 by line 34.

The rate of flow of chilled dewaxed oil through the aforesaid heatexchangers to chill the warm wax bearing oil is controlled by pump 31which may be set to maintain the rate necessary to progressively coolthe incoming warm oil at a desired temperature gradient.

The partially chilled wax bearing oil is chilled in heat exchanger 24 byintense refrigerant in the following way. Liquid volatile refrigerantsuch as ammonia is fed into accumulator 5| where it is allowed tovaporize at a pressure, e. g., 6 lbs. per square inch absolute. Thecirculation of the ammonia is caused by the rise in temperature in coils52 of the heat exchanger 24 and by such vaporization as may occur inthese coils.

Where, for example, ammonia is used as a refrigerant and is released at6 lbs. per square inch absolute both in cooler 4| and accumulator 5|,cooler 4| and accumulator 5| may be arranged in parallel with respect toa common compressor 53. The compressed ammonia passes from compressor 53by the line 54. It is taken by lines 55 and 56 through control valve 51to cooler 4| where it is released. The ammonia vapor is reconveyed tothe suction side of the compressor 53 from cooler 4| by lines 58 and 59.Ammonia from the compressor 53 is taken to the accumulator 5| by lines54, 6|] and 6| through control valve 62 which releases the ammonia intothe accumulator 5|. The ammonia vapor from accumulator 5| is reconveyedto the suction side of the compressor 53 by lines 63 and 69.

Ammonia which is released in cooler 39, for example at 15 lbs. persquare inch absolute, is compressed by compressor 64 from which itpasses by lines 55 and 66 through control valve 61 into cooler 39. Fromcooler 39 ammonia vapor may be reconveyed to the suction side ofcompressor 64 by line 68.

The ammonia compressed in compressors 53 and 64 may be condensed incondensers 69 and T0 and stored in receptacles l and 72. Valves 5'! andBl which admit the ammonia vapor into coolers 4| and 39 respectively andvalve 62 which admits vapor into accumulator 5| may be operated by floatcontrol for maintaining a constant level of ammonia in coolers 4| and 39and in ac cumulator 5|, thus securing automatic regulation.

By the process and apparatus above described, wax bearing oil at about1.00 F. may be gradually cooled to a temperature of -40 F. at whichtemperature the wax will have precipitated so that it may be readilyremoved as by centrifugal separation from the oil. By chilling with theapparatus above described and centrifugally separating the wax therefroma lubricating oil hav ing a cold test of 0 F. to 5 F. may be produced;Oils having a higher cold test may be obtained by operating at highertemperatures. In some cases, on the other hand, it may be advisable tooperate at lower ammonia pressures and temperatures in order to obtain alower cold test. While the oil may contain some residual wax which hasnot been precipitated by the chilling and which has not been removedtherefrom, it has nevertheless been freed of sufficient wax to producean oil of desired cold test, and oil from which wax has been thusremoved is in this sense wax-freed.

According to the above process and apparatus, the incoming warm oil maybe chilled by the chilled dewaxed oil to a temperature which permits thepartially chilled oil to be subjected directly to an intense refrigerantWithout shock chilling which latter refrigerant will complete theprocess of chilling to the desired low temperature. By controlling theflow of chilled dewaxed oil through heat exchangers l4 to 2| by pump 31,a progressive gradual and continuous chilling of the warm oil flowing incounterfiow therewith may be accomplished without shock chilling, toprecipitate the wax in the best physical state for separation from theoil.

While specific forms of apparatus and specific methods of operation havebeen set forth above, it is to be understood that such specificdescription has merely been by way of illustration of this invention andthat the same may be modified in many details without departing from thescope of this invention.

I claim:

1. A process of. dewaxing oil by chilling said oil to precipitate waxand removing precipitated wax, which comprises separating wax fromchilled oil by centrifugal force affording wax-freed oil separated fromwax, chilling the warm waxbearing oil before and chilling the wax-freedoil after the separation of wax therefrom by heat exchange with avolatile liquid refrigerant released both before and after the'waxseparation step at substantially similar pressures and compressed fromsaid pressures by a common compresssor, and bringing said rechilledwax-freed oil into indirect counterflow heat exchange with warmwax-bearing oil while the wax-freed oil is at a lower temperature thanthe temperature thereof when taken from the wax separation step andwhile the wax-freed oil contains substantially less wax than the warmwax-bearing oil.

2. A process of dewaxing oil by chilling said oil to precipitate waxtherefrom and removing precipitated wax, which comprises chilling waxbearing oil by liberating compressed volatile liquid refrigerant at agiven pressure, separating dewaxed oil from the chilled wax-bearing oil,chilling the dewaxed oil by releasing a compressed volatile liquidrefrigerant at a higher pressure than that used in chilling the waxbearing oil, then further chilling the dewaxed oil by releasingcompressed volatile liquid refrigerant at a pressure substantially thesame as that used in chilling the wax bearing oil, and then using thechilled dewaxed oil to partially chill warm wax bearing oil.

3. A process of dewaxing oil by chilling said oil to precipitate waxtherefrom and removing precipitated wax, which comprises compressing avolatile liquid refrigerant with a single compressor, chilling waxbearing oil by heat exchange with said volatile liquid refrigerant uponreleasing a portion of said refrigerant at a given pres sure, separatingdewaxed oil from the chilled wax bearing oil, chilling said dewaxed oilby direct heat exchange with said volatile liquid refrigerant uponreleasing another portion of refrigerant at a like pressure, andreturning said released refrigerant to said compressor.

4. In a process of dewaxing oil wherein wax bearing oil is chilled toprecipitate wax therefrom and cold dewaxed oil is separated from theprecipitated Wax and comprised in a refrigerant used to chill warm waxbearing oil by heat exchange, the steps comprising adjusting the heatabsorptive characteristics of. the refrigerant comprising the colddewaxed oil in relation to the heat giving characteristics of the warmwax bear ing oil which is chilled thereby so as to cause the refrigerantcomp-rising cold dewaxed oil to be warmed at substantially the same ratethat the warm wax bearing oil is cooled during said heat exchange andchilling said refrigerant comprising cold dewaxed oil from the waxseparation step prior to bringing said refrigerant into heat exchangewith warm wax bearing oil.

5. In apparatus for dewaxing oil, means for passing dewaxed oil inindirect heat-exchange relation and out of contact with wax-containingoil, means for separating precipitated wax from wax-containing oil andadapted to receive cold wax-containing oil from said heat-exchangingmeans, a tank adapted to receive cold dewaxed oil from said separatingmeans, a pipe for conducting to said tank dewaxed oil flowing from saidheat-exchanging means, means dependent upon the level of oil in saidtank for controlling flow through said last-named pipe to said tank, achiller and means for passing dewaxed oil from said tank to said chillerand from said chiller to said heat-exchanging means.

6. A process of dewaxing oil by chilling said oil to precipitate waxtherefrom and removing precipitated Wax, which comprises separating acold dewaxed oil from a wax-bearing oil by a dewaxing step, adding tosaid dewaxed oil from said dewaxing step additional dewaxed oil to forma mixture, bringing said mixture into counterflow heat exchange withwarm wax-bearing oil, vary ing the amount of dewaxed oil added to thede- Waxed oil taken from the wax separation step in accordance withvariations in the amount of dewaxed oil from the wax separation step soas to maintain the amount of the mixture in counterfiow with warmwax-bearing oil substantially constant and bringing the mixture toeffective chilling temperature by means of a refrigerating operationsubsequent to the dewaxing step.

' MALCOLM H. TU'I'I'LE.

